This invention relates generally to dental apparatus for use in endodontic procedures and more particularly to a tool and hand piece suitable for retrofill cavity preparation, that is, preparation of a root cavity for filling from the bottom, by access through an opening provided in the jawbone.
In root canal surgery, the space containing the pulp is opened by drilling into the tooth from the top. The pulp is then removed and a suitable material is used to fill the entire internal volume of the tooth. However, if pain persists or if problems develop subsequently to cause the patient to feel pain in the tooth, it may be necessary to drill into the bottom of the tooth root which is seated in the jawbone. Such drilling is accomplished from the side, through the gums and jawbone. The tip or bottom of the root is removed and the bottom of the root canal is bored out and is subsequently filled with a filler material.
In the past, such bore has been made by an vibratory instrument operating at ultrasonic frequencies. Vibrations are induced in the tool by a mechanism, typically including a piezoelectric element, in a hand piece to which the tool is mounted, and which is adapted to be held by the dental surgeon. Rotary drilling bits are also sometimes used in place of, or in conjunction with, tools operating with vibratory motion. Because of the various locations in the mouth where root canal surgery may be required and because of the relative inaccessibility of many of these areas and the small space between cheek and jawbone, tools of many different shapes have been constructed to accommodate the various tooth locations so that the bottom of the root can be reached for retrofill cavity preparation regardless of the tooth's location. No single tool is known which is sufficiently versatile to operate at all of the tooth locations. Many possibilities for misaligning a drilled cavity, or for over-enlargement or excessive depth of a drilled cavity, are present. Such hazards are especially prevalent when using devices that vibrate at ultrasonic frequencies, since a small deviation from an intended path of operation can quickly and undesirably remove relatively large quantities of tooth material. Among others, the risk of an unintended breaking through of the side wall of a tooth is increased at ultrasonic frequencies. At best, operation of these tools involves very delicate and time consuming procedures.
Further, when operating at ultrasonic speeds with conventional tools, it is difficult to avoid enlarging the entrance to the cavity drilled at the bottom of the root such that the cavity becomes conical in shape, that is, increasing in diameter toward the bottom of the root. Such a conical shape, when filled from the bottom, results in a filling which may easily be dislodged. A straight, i.e. cylindrical, bore into the bottom of the tooth is preferred, since the friction from the parallel side wall of the bore aids in maintaining the filler material in place.
In the prior art, U.S. Pat. No. 5,094,617, issued Mar. 10, 1992, provides an ultrasonic tool having a conical working end that is connected at an angle to an elongated stem. Stems of many different shapes, both smoothly curved and also bent at clearly defined angles, are disclosed. Regardless of shape, the stem is received coaxially in a compatible tool holder of a hand piece for a dental retrofill instrument. Longitudinal ultrasonic vibrations generated in the hand piece are transmitted to the stem and to the conical working end of the tool, which is applied to a patient's tooth. The above-mentioned hazards associated with ultrasonic tools affect usage of the tools of the type disclosed in U.S. Pat. No. '617. The need for numerous tools, each of a different shape so as to access teeth of different locations can be an inconvenience to the surgeon.